Computer-implemented semi-supervised learning systems and methods

ABSTRACT

Computer-implemented systems and methods for determining a subset of unknown targets to investigate. For example, a method can be configured to receive a target data set, wherein the target data set includes known targets and unknown targets. A supervised model such as a neural network model is generated using the known targets. The unknown targets are used with the neural network model to generate values for the unknown targets. Analysis with an unsupervised model is performed using the target data set in order to determine which of the unknown targets are outliers. A comparison of list of outlier unknown targets is performed with the values for the unknown targets that were generated by the neural network model. The subset of unknown targets to investigate is determined based upon the comparison.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ApplicationSer. No. 60/902,380, (entitled “Computer-Implemented Semi-supervisedLearning Systems And Methods” and filed on Feb. 20, 2007), of which theentire disclosure (including any and all figures) is incorporated hereinby reference.

This application contains subject matter that may be considered relatedto subject matter disclosed in: U.S. Application Ser. No. 60/902,378,(entitled “Computer-Implemented Modeling Systems and Methods foranalyzing Computer Network Intrusions” and filed on Feb. 20, 2007); U.S.Application Ser. No. 60/902,379, (entitled “Computer-Implemented Systemsand Methods For Action Determination” and filed on Feb. 20, 2007); U.S.Application Ser. No. 60/902,381, (entitled “Computer-Implemented GuidedLearning Systems and Methods for Constructing Predictive Models” andfiled on Feb. 20, 2007); U.S. Application Ser. No. 60/786,039 (entitled“Computer-Implemented Predictive Model Generation Systems And Methods”and filed on Mar. 24, 2006); U.S. Application Ser. No. 60/786,038(entitled “Computer-Implemented Data Storage For Predictive ModelSystems” and filed on Mar. 24, 2006); and to U.S. ProvisionalApplication Ser. No. 60/786,040 (entitled “Computer-ImplementedPredictive Model Scoring Systems And Methods” and filed on Mar. 24,2006); of which the entire disclosures (including any and all figures)of all of these applications are incorporated herein by reference.

TECHNICAL FIELD

This document relates generally to constructing and using computerpredictive models and more particularly to using semi-supervisedlearning systems and methods for generating predictive models.

BACKGROUND

Computer predictive models have found applicability in many diverseareas. However, difficulty arises in using predictive models when thetraining targets are not fully known. A non-limiting example wherepredictive models encounter unknown targets is when predictive modelsare to assess whether fraud may have occurred with respect tomonetary-related transactions. Current predictive model approaches havedifficulty in discerning legitimate monetary-related transactions fromfraudulent ones.

SUMMARY

In accordance with the teachings provided herein, systems and methodsfor operation upon data processing devices are provided for performingsemi-supervised learning. For example, a method and system can beconfigured to receive a target data set, wherein the target data setincludes known targets and unknown targets. A supervised model such as aneural network model is generated using the known targets. The unknowntargets are used with the neural network model to generate values forthe unknown targets. Analysis with an unsupervised model (e.g., using anapproach such as outlier detection analysis) is performed using thetarget data set in order to determine which of the unknown targets areoutliers. A comparison of the list of outlier unknown targets isperformed with the values for the unknown targets that were generated bythe neural network model. The subset of unknown targets to investigateis determined based upon the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting a computer-implemented system forconstructing predictive models.

FIG. 2 is a block diagram depicting neural network training combinedwith an outlier detection process.

FIG. 3 is a process flow diagram depicting predictive model constructionand use.

FIG. 4 is a process flow diagram depicting application of a neuralnetwork to generate scores.

FIGS. 5 and 6 are process flow diagrams depicting techniques forperforming outlier detection.

FIG. 7 is a flowchart depicting an operational scenario for using anon-linear replicator neural network (e.g., a compression neuralnetwork) in determining outliers.

FIG. 8 is a process flow diagram depicting generation of a rank orderlist from an outlier detection process.

FIG. 9 is a process flow diagram depicting an iterative training processfor improving a neural network model.

FIG. 10 is a process flow diagram depicting an iterative trainingprocess for improving an outlier detection process.

FIG. 11 is a process flow diagram depicting a system for analyzingfinancial or monetary type activities with respect to whether fraud mayhave occurred.

FIG. 12 is a process flow diagram depicting the combination of resultsfrom a neural network model with results from an outlier detectionprocess.

FIG. 13 is a block diagram depicting a networked environment whereinusers can interact with a predictive model construction system.

FIG. 14 is a block diagram depicting a stand-alone computer environmentwherein a user can interact with a predictive model construction system.

DETAILED DESCRIPTION

FIG. 1 depicts at 30 a computer networked environment wherein users 32can interact with a predictive model construction system 34. System 34allows the users 32 to build predictive models even when targets 42 ofthe modeling process are only partially known. This can be useful inmany different situations, such as in semi-supervised learningsituations.

Semi-supervised situations involve generation of predictive modelstypically (but not always) by means of a small amount of labeled dataand a large amount of unlabeled data (e.g., collectively target data set42). Semi-supervised situations can arise because the cost associatedwith the labeling process may render a fully labeled training setimpractical, whereas acquisition of unlabeled data is relativelyinexpensive. In such situations, semi-supervised learning can be ofgreat practical value.

The users 32 can interact with the predictive model construction system34 through a number of ways, such as over one or more networks 36. Aserver 38 accessible through the network(s) 36 can host the predictivemodel construction system 34. Data store(s) 40 can store the data to beanalyzed (e.g., target data set 42) as well as any intermediate or finaldata calculations and data results.

The predictive model construction system 34 can be a web-based tool thatprovides users with flexibility and functionality for generatingpredictive models when the targets 42 are only partially known.Moreover, the predictive model construction system 34 can be usedseparately or in conjunction with other software programs, such as withother predictive model construction techniques.

With reference to FIG. 2, neural network training 50 combined with anoutlier detection process 52 allow for the identification of whichtargets in the target data set 42 should be focused upon in order toascertain the true (or at least a more accurate) value of the targets.The increased knowledge for some of the targets results in an evolutionin the fidelity of the model's or models' predictive capability. Morespecifically, model training evolves from a state where the targets arepartially known to a state where at least more of the targets have beenidentified.

FIG. 3 illustrates a process flow by which predictive model constructioncan be performed using the target data set 42. As discussed above, thetarget data set 42 contains only a partial set of known targets (e.g.,known targets 100 and unknown targets 110). As an example of one of theuses, the process flow can help in determining which of the potentiallymany unknown targets should be focused upon in order to determine thetrue values for these unknown targets.

Process 50 constructs models for predicting target values for theentries contained in the target data set 42. Many different types ofpredictive models can be constructed, such as artificial neural networkpredictive models. An artificial neural network is constructed ofinterconnecting neurons designed to model the target(s) and whichchanges its structure based on how it is trained, such as through thetraining process 50. More specifically, neural networks are non-linearstatistical data modeling tools. They can be used to model complexrelationships between inputs and targets or to find patterns in data.

The training process 50 begins with a set of interconnected nodes andalters the strength (e.g., weights) of the connections in the network toproduce outputs. The training process 50 is provided with the input dataabout the target data set 42 and a cost function to be minimized. Thecost function can be any function of the target values and predictedtarget values from the model under construction, such as the norm of thedifference between the predicted and original target values. With theinput data and the cost function, process 50 generates a neural networkmodel using the known targets 100 (or at least a portion of the knowntargets 100). The unknown targets 110 (or at least a portion of theunknown targets 110) are used with the generated neural network model togenerate values (i.e., results 130) for the unknown targets 110.

An outlier detection process 52 is performed using the target data set42 for determining which of the unknown targets 110 are outliers. Anunknown target being identified as an outlier by process 52 is anindication of anomalous activity, such as the possibility that fraud mayhave occurred.

In training process 52, both the input data set and the output data setare the target data set 42. The learning process tries to reproduce theinput data as the target. Let the vector x=(x₁, x₂, . . . x_(p))^(T)represent an observation with p inputs to the unsupervised learningprocess with a mean μ and covariance Σ. Let the vector y=(y₁, y₂, . . .y_(p))^(T) represent the same observation with p outputs from theunsupervised learning process. The cost function can be any function ofthe input data and target output of the model under construction—such asin this example, the Mahalanobis distance between the inputs and outputswhich is defined as √{square root over ((x−y)^(T)Σ⁻¹(x−y))}{square rootover ((x−y)^(T)Σ⁻¹(x−y))}. The difference between the inputs and outputsis also defined as the reconstruction error of the unsupervised learningprocess and can be represented as E=(x−y). The Mahalanobis distancebased reconstruction error can thus be defined as √{square root over(E^(T)Σ⁻¹E)}. The covariance matrix can be expressed in terms ofeigenvalue matrix Λ and eigenvector U as Σ=UΛU^(T). Therefore, √{squareroot over (E^(T)Σ⁻¹E)} can be computed from √{square root over((EU)^(T)Δ⁻¹(EU))}{square root over ((EU)^(T)Δ⁻¹(EU))}. Σ can be noisy.The computation of the reconstruction error can be done by using thefirst m eigenvalues Λ of the covariance matrix Σ. An alternate approachis to use the first m eigenvalues and a small value for the remainingeigenvalues. A more general approach could be to weight the differenteigenvalues differently in computing the reconstruction error. Theinputs with the highest reconstruction error are deemed to be anomalousinputs.

Process 140 performs a comparison between the list of unknown targets(that have been identified as outliers) and the values 130 for theunknown targets that were generated by the neural network model. Thesubset 150 of unknown targets to investigate is determined based uponthe comparison by process 140.

FIGS. 4 and 5 provide additional details respectively for the neuralnetwork training process 50 and the outlier detection process 52. Withreference to FIG. 4, results 130 are generated when the neural networkis applied at process 200 to the unknown target data set 110. Forexample, if the neural network is to detect whether fraud has occurredwith respect to a financial or monetary transaction, then process 200can generate target value scores for the unknown target data set 110 asthe results 130 of the neural network.

The scores of the neural network model can assume a number of differentformats. As an illustration, the scores can be binary in nature (e.g., avalue of 1 to indicate that a transaction constitutes fraud; and a valueof 0 to indicate that fraud has not occurred). The scores could alsoencompass a range of values. For example, a continuous range from 0-100can indicate the degree by which an item in the target data set 42 canbe considered fraudulent, wherein a value of 0 can establish the lowerend of the fraud spectrum (i.e., not a fraud event) and a value of 100can establish the upper end of the fraud spectrum.

FIG. 5 illustrates that the outlier detection process 52 can detectwhether an unknown target should be considered an outlier with respectto the other unknown targets by performing processes 300 and 310.Process 300 compresses the data related to the unknown targets 110 byreducing the multi-dimensional data set to a lower dimension. Process310 then reverses the compression process by expanding the data set fromthe lower dimension back to a higher dimension. Outliers can then bedetected based upon how the data set performed during the compressionand uncompression processes 300 and 310.

Different techniques are available in order to perform the compressionand uncompression processes 300 and 310 such as by using nonlinearreplicator neural networks (e.g., autoregressive neural networks, etc.)as shown at 350 in FIG. 6. Non-linear replicator neural networks aregenerally known in the art and discussed in such references as: S.Hawkins, H. X. He, G. J. Williams, and R. A. Baxter “Outlier detectionusing replicator neural networks,” Proceedings of the FifthInternational Conference and Data Warehousing and Knowledge Discovery2002; G. J. Williams, R. A. Baxter, H. X. He, S. Hawkins, and L. Gu “Acomparative study of RNN for outlier detection in data mining,”Proceedings of the 2002 IEEE International Conference on Data Mining;and O. Abdel-Wahhab and M. Fahmy, “Image compression using multi-layerneural networks,” Proceedings of the 2nd IEEE Symposium on Computers andCommunications (ISCC 1997).

FIG. 7 depicts an operational scenario for using a nonlinear replicatorneural network in determining outliers based upon an input set ofunknown targets. With reference to FIG. 7, a nonlinear replicator neuralnetwork compresses at step 400 the input unknown target data into alower dimensional representation. Step 410 reverses the process byuncompressing the intermediate details back into the originaldimensional representation. Step 420 examines the error that may haveoccurred between the uncompressed form and input data. The error isgreater for those target values that had difficulty in being compressedinto the lower dimensional representation. Target outliers aredetermined based upon the amount of target error that was determined instep 420.

As shown in FIG. 8, the results 120 of the outlier detection process 52can be a rank order list. The rank order list contains the unknowntargets (that were determined to be outliers) in an order dictated bythe error amount that they exhibited from the compression anduncompression processes. In other words, the unknown targets thatexhibited the greatest amount of error would be ranked higher in theoutlier list than the unknown targets that did not exhibit as mucherror. The results 130 of the neural network training process 50 canalso be a rank order list format.

Process 140 compares the results 130 (e.g., the unknown target scores)from the neural network with the rank order list from the outlierdetection process 52. The comparison process 140 can use output subsetcriteria 500 in determining which of the unknown targets should beincluded in the subset 150 of unknown targets to investigate. As anexample, the output subset criteria 500 can specify that the subset 150should include only those unknown targets that have a relatively highscore as determined by the neural network model as well as those thatwere highly ranked as outliers by the outlier detection process. Thecombination of the analyses performed by the neural network and by theoutlier detection process enhances the fidelity of the selection ofwhich of the unknown targets constitutes anomalous behavior. It shouldbe understood that many different types of criteria can be used in orderto determine the subset of unknown targets to investigate and should bebased upon the application at hand.

FIG. 9 depicts that an iterative training process can be employed forimproving the neural network training. For example, after the subset 150of unknown targets to investigate has been established, process 600 caninvestigate the true status or values of the unknown targets in thesubset 150.

The investigation process 600 is resource efficient because theinvestigation (at this stage) only needs to focus on the subset 150 andnot the entire (and potentially large) corpus of unknown targets. As anexample of process 600, analyzing the subset 150 can include examinationby human analysts of the unknown targets to determine which targetswithin the data subset 150 constitute anomalous behavior.

In addition to or as a supplement to manual investigation, analysis ofthe target subset 150 can include examination of the subset 150 byanother software program that uses more resource intensive techniques todetermine a more accurate set of values for the unknown targets in thesubset 150.

In any event, process 600 results in more accurate target values beingproduced for the data subset 150. The target results are fed intoprocess 50 so that the neural network model can be improved whichresults in more accurate results 130 for use by the comparison process140 in subsequent iterations.

FIG. 10 illustrates then the retraining process can also be applied tothe outlier detection process 52. After process 600 has investigated thesubset 150 of unknown targets and ascertained the true values for thesubset 150, these target values 610 can be made available to improve at700 the outlier detection process. The nonlinear replicator neuralnetwork that was used in the outlier detection process 52 can beimproved by training the model based upon the target values that are nowknown for the subset.

The predictive model construction approaches described herein can beutilized for many different purposes where target values are unknown.For example, predictive models can be constructed in order to analyzewhether fraud may have occurred with respect to a financial transaction.FIG. 11 depicts a computer-implemented system for analyzing financial ormonetary type activities with respect to whether fraud may have occurred(e.g., purchase card fraud or tax evasion fraud).

The target data set 800 includes both known targets 802 and unknowntargets 808. The known targets 802 in this example include known fraudtargets 804 or instances of fraud (e.g., an entity had filed a false taxreturn; an entity had used a stolen credit card to purchase an item;etc.) as well as known non-fraud targets (e.g., an entity had filed acorrect tax return; an entity had made a legitimate credit cardpurchase; etc.). In this example, the number of legitimate type targetsoverwhelmingly outnumbers the known fraud targets. The unknown targets808 constitute entities, such as individuals or organizations, whosetransactions (e.g., filing a tax return; making a credit card purchase;etc.) do not contain an indication of whether fraud has occurred.

As discussed above, the target data set 800 contains only a partial setof known targets (e.g., known targets 802 and unknown targets 808).Process 810 trains a model (e.g., neural network) for predicting valuesor scores that are indicative of whether fraud has occurred with respectto the known targets 802.

With the input data and the cost function, process 810 generates aneural network model using the known targets 802. The unknown targets808 are used with the generated neural network model to generate values(i.e., fraud-indicative scores 830) for the unknown targets 808.

An outlier detection process 820 is performed using the target data set800 in order to determine which of the unknown targets 808 are outliers.An unknown target being identified in the results 840 as an outlier byprocess 820 is an indication of fraudulent activity. More specificallyin this example, the results 840 of the outlier detection process 820can be a rank order list. The rank order list contains the unknowntargets that were determined to be outliers ordered by the error amountthat they exhibited from the compression and uncompression processes.The unknown targets exhibiting a higher amount of error are consideredmore likely to involve fraudulent activity than the unknown targets thatexhibit a smaller amount of error.

Process 850 performs a comparison between the list of unknown targets(that have been identified as outliers) and the scores 830 for theunknown targets that were generated by the neural network model. Thesubset 870 of unknown targets to investigate is determined based uponthe comparison by process 850.

Process 850 compares the fraud-indicative scores 830 from the neuralnetwork with the rank order list from the outlier detection process 820.The comparison process 850 uses subset criteria 860 in determining whichof the unknown targets should be included in the subset 870 of unknowntargets to investigate. In this example, the subset criteria 870specifies that the subset 860 should include only those unknown targetsthat have a relatively high score as determined by the neural networkmodel as well as those that were highly ranked as outliers by theoutlier detection process.

Process 880 performs an investigation of the unknown targets that passedthe fraud-indicative criteria 860. As a result of the investigation 880,the true target values become known for the subset 870 and are used toretrain the neural network at 810. The retrained neural network is thenapplied to the remaining unknown targets in the target data set 800 inorder to generate new fraud indicative scores.

Similarly, the target values 890 that are known for the subset 870 canalso be used to refine the outlier detection process as indicated in1000. The improved outlier detection process 820 performs outlierdetection upon the remaining unknown targets 808 in order to produce anew fraud-indicative outlier list. Process 850 then uses the newfraud-indicative scores as well as the new fraud-indicative scoresgenerated by process 810 when it is to perform its comparisonoperations. Process 850 results in a new subset of unknown targets toinvestigate. The investigation and retraining operations can continueuntil the models have reached a particular level of precision and/oruntil no more investigations are desired.

While examples have been used to disclose the invention, including thebest mode, and also to enable any person skilled in the art to make anduse the invention, the patentable scope of the invention is defined byclaims, and may include other examples that occur to those skilled inthe art. Accordingly the examples disclosed herein are to be considerednon-limiting. As an illustration, FIG. 12 shows that the results 120 and130 that are respectively generated via a processes 52 and 50 can becombined by process 1100. The combination of the results can be used toconstruct a more robust overall predictive model to determine whether anevent or activity constitutes anomalous behavior. More specifically, thecombination of the results can be achieved through optimizing thecontributions of the results from processes 50 and 52 to the finaloverall model in terms of the model performance on known target dataset.

As another illustration, the systems and methods disclosed herein coulduse different types of models as supervised models and unsupervisedmodels. For example, linear regression models and logistic regressionmodels can be used as supervised models in the disclosed operationalscenarios; and principal component analysis type models can be used asunsupervised models in the disclosed operational scenarios.

As yet another illustration, the systems and methods disclosed hereinmay be implemented on various types of computer architectures, such asfor example on a networked system, on a single general purpose computer,etc. For example, FIG. 13 depicts a networked environment wherein users32 can interact with a predictive model construction system 34. The sameserver or different servers can contain various software instructions1200 (e.g., software instructions for neural network training, softwareinstructions for outlier detection, etc.) or modules of the predictivemodel construction system 34. Data store(s) 40 can store the data to beanalyzed as well as any intermediate or final data calculations and dataresults of such software instructions or modules.

It should be understood that the analytical systems described herein(e.g., tax fraud analysis system, purchase card fraud analysis system,etc.) can be implemented in other ways, such as on a stand-alonecomputer for access by a user as shown at 1300 in FIG. 14.

It is further noted that the systems and methods may include datasignals conveyed via networks (e.g., local area network, wide areanetwork, internet, combinations thereof, etc.), fiber optic medium,carrier waves, wireless networks, etc. for communication with one ormore data processing devices. The data signals can carry any or all ofthe data disclosed herein that is provided to or from a device.

Additionally, the methods and systems described herein may beimplemented on many different types of processing devices by programcode comprising program instructions that are executable by the deviceprocessing subsystem. The software program instructions may includesource code, object code, machine code, or any other stored data that isoperable to cause a processing system to perform methods describedherein. Other implementations may also be used, however, such asfirmware or even appropriately designed hardware configured to carry outthe methods and systems described herein.

The systems' and methods' data (e.g., associations, mappings, etc.) maybe stored and implemented in one or more different types ofcomputer-implemented ways, such as different types of storage devicesand programming constructs (e.g., data stores, RAM, ROM, Flash memory,flat files, databases, programming data structures, programmingvariables, IF-THEN (or similar type) statement constructs, etc.). It isnoted that data structures describe formats for use in organizing andstoring data in databases, programs, memory, or other computer-readablemedia for use by a computer program.

The systems and methods may be provided on many different types ofcomputer-readable media including computer storage mechanisms (e.g.,CD-ROM, diskette, RAM, flash memory, computer's hard drive, etc.) thatcontain instructions (e.g., software) for use in execution by aprocessor to perform the methods' operations and implement the systemsdescribed herein.

The computer components, software modules, functions, data stores anddata structures described herein may be connected directly or indirectlyto each other in order to allow the flow of data needed for theiroperations. It is also noted that a module or processor includes but isnot limited to a unit of code that performs a software operation, andcan be implemented for example as a subroutine unit of code, or as asoftware function unit of code, or as an object (as in anobject-oriented paradigm), or as an applet, or in a computer scriptlanguage, or as another type of computer code. The software componentsand/or functionality may be located on a single computer or distributedacross multiple computers depending upon the situation at hand.

It should be understood that as used in the description herein andthroughout the claims that follow, the meaning of “a,” “an,” and “the”includes plural reference unless the context clearly dictates otherwise.Also, as used in the description herein and throughout the claims thatfollow, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise. Finally, as used in the description hereinand throughout the claims that follow, the meanings of “and” and “or”include both the conjunctive and disjunctive and may be usedinterchangeably unless the context expressly dictates otherwise; thephrase “exclusive or” may be used to indicate situation where only thedisjunctive meaning may apply.

It is claimed:
 1. A processor-implemented method for determining asubset of unknown targets to investigate, comprising: receiving a targetdata set; wherein the target data set includes known targets and unknowntargets; generating a neural network model using the known targets;using the unknown targets with the neural network model to generatevalues for the unknown targets; performing outlier detection analysisusing the target data set in order to determine which of the unknowntargets are outliers; performing a comparison of list of outlier unknowntargets with the values for the unknown targets that were generated bythe neural network model; wherein the subset of unknown targets toinvestigate is determined based upon the comparison.
 2. The method ofclaim 1, wherein the target data set is indicative of entities toinvestigate with respect to fraud.
 3. The method of claim 2, wherein thefraud includes tax evasion fraud or purchase card fraud.
 4. The methodof claim 2, wherein the values for the unknown targets that weregenerated by the neural network model are scores indicative of whetherfraud has occurred.
 5. The method of claim 1, wherein the performing ofthe outlier detection analysis includes compressing at least a portionthe unknown targets into a lower dimensional representation anduncompressing intermediate results of the compressing process into ahigher dimensional representation; determining whether an unknown targetis an outlier based error that exists between the uncompressed form andthe unknown target.
 6. The method of claim 5, wherein said compressingis performed by using a compression neural network approach.
 7. Themethod of claim 1, wherein the performing of the outlier detectionanalysis includes using a nonlinear replicator neural network approachto determine which of the unknown targets are outliers.
 8. The method ofclaim 1, wherein the list of outlier unknown targets is a rank orderlist of the unknown targets that was generated through use of acompression neural network approach.
 9. The method of claim 1, whereinthe performing of the comparison includes comparing based upon apre-specified criterion or criteria the list of outlier unknown targetswith the values for the unknown targets that were generated by theneural network model.
 10. The method of claim 9, wherein thepre-specified criterion or criteria contain criterion or criteria forincluding in the subset of unknown targets to investigate those unknowntargets that have a value that satisfies a value scoring threshold andthat have been determined to be outliers by the outlier detectionanalysis.
 11. The method of claim 1, wherein targets in the determinedsubset of unknown targets are investigated; wherein the targets in thedetermined subset become known because of the investigation.
 12. Themethod of claim 11 further comprising: retraining the neural networkusing the known targets and the targets that have become known becauseof the investigation.
 13. The method of claim 12 further comprising:using the retrained neural network upon the unknown targets in order togenerate values for the unknown targets.
 14. The method of claim 13further comprising: performing a second outlier detection analysis inorder to determine a second list of which of the unknown targets areoutliers; performing a second comparison of the second list of outlierunknown targets with the values for the unknown targets that weregenerated by the retrained neural network model; wherein a second subsetof unknown targets to investigate is determined based upon the secondcomparison.
 15. The method of claim 1 further comprising: combiningvalues for the unknown targets that were generated by the neural networkmodel with outlier results generated by the outlier detection process inorder to optimize the overall model performance.
 16. The method of claim1, wherein an unknown target being identified as an outlier by theoutlier detection process is an indication of anomalous activity. 17.The method of claim 16, wherein an unknown target being identified as anoutlier by the outlier detection process is an indication of fraudulentactivity.
 18. A data signal that is transmitted using a network, whereinthe data signal includes the subset of unknown targets to investigate ofclaim 1; wherein the data signal comprises packetized data that istransmitted across the network.
 19. A processor-implemented system fordetermining a subset of unknown targets to investigate, comprising: adata store to store a target data set; wherein the target data setincludes known targets and unknown targets; model generation softwareinstructions configured to generate a neural network model using theknown targets; wherein the unknown targets are used with the neuralnetwork model to generate values for the unknown targets; softwareinstructions to perform outlier detection analysis using the target dataset in order to determine which of the unknown targets are outliers;comparison software instructions configured to perform a comparison oflist of outlier unknown targets with the values for the unknown targetsthat were generated by the neural network model; wherein the subset ofunknown targets to investigate is determined based upon the comparison.20. Computer software stored on one or more computer readable mediums,the computer software comprising program code for determining a subsetof unknown targets to investigate, said method comprising: receiving atarget data set; wherein the target data set includes known targets andunknown targets; generating a neural network model using the knowntargets; using the unknown targets with the neural network model togenerate values for the unknown targets; performing outlier detectionanalysis using the target data set in order to determine which of theunknown targets are outliers; performing a comparison of list of outlierunknown targets with the values for the unknown targets that weregenerated by the neural network model; wherein the subset of unknowntargets to investigate is determined based upon the comparison.